1. Field of the Invention
The present invention relates to a vehicle-mounted power supply system for charging a storage battery and supplying power to electrical loads.
2. Description of the Related Art
As disclosed in Japanese Patent Publications 6-296332 and 2002-238103, a vehicle-mounted power supply system is controlled to generate electricity according to the driving condition of the vehicle for improving fuel consumption and emission of noxious gases. In particular, the vehicle-mounted power supply system is operated in different modes according to the driving condition of the vehicle. During deceleration, power regeneration is performed by converting the momentum of the vehicle to electric energy and returning it to a storage battery, and during acceleration, power generation is shutdown to utilize the recaptured electric energy instead of generating power. The vehicle-mounted power supply system usually comprises a first storage battery charged by an automotive generator and a second storage battery connected to an electrical load. A power converter is provided between the first and second storage batteries. Voltage variations can occur in the second storage battery depending on the amount of electrical load of the vehicle. The power converter monitors the voltage of the second battery and adaptively controls the amount of electric power transferred from the first battery to the second battery when the monitored voltage deviates from a reference voltage. The power converter operates successfully to maintain the second battery voltage at a substantially constant level if the amount of electrical power consumption is within its adaptive control range.
However, intermittent power regeneration and shutdown could produce a large variation in the electrical power consumption of the vehicle and such variation could eventually exceed beyond the adaptive control range of the power converter. Thus, the voltage supplied to the headlights and air-conditioning system will undergo large variations, causing such unfavorable situations as fluctuating illumination and varying blower-motor speed. The problem may be overcome by increasing the adaptive control range of the power converter. However, it only adds to the size and capacity of the power converter. Additionally, such unfavorable situations may be avoided by preventing the power supply system from operating in power-shutdown and regeneration modes. However, the advantageous features of less fuel consumption and reduced emission of harmful gases would be lost.
Therefore, a need does exist to provide a vehicle-mounted power supply system capable of supplying a constant power voltage to electrical loads under varying vehicle-operating conditions.